Page 26 - 201902 SCA February 2019 Volume 56 Number 1

Technical ARTICLE

Studies of pre-treatment in various woods with high

performance light stabilizers

By Yung-Chi Yang, Pei-Yun Lee, Yin-Ting Lai, Miles Hsieh, Chung-Han Lu, Dr. Yao-Hsing Huang
Specialty Chemical Business Unit, Everlight Chemical Industrial Corporation.

ABSTRACT Due to higher lignin content in softwoods (25–35%)
Lignin, when exposed to the sunlight, can easily be to hardwoods (18–25%), theoretically, Eversorb®
degraded. To preserve the beauty of wood grain, SB pre-treatment could offer better protection to
waterborne clear coats containing UV absorbers and softwoods. Our data supports the hypothesis; pre-
light stabilizers are commonly applied to the surface treatment with Eversorb® SB provides significant
for protection. However, the effectiveness of such protection in softwoods (Southern Pine and Douglas
application is limited. According to our studies, pre- fir) than in hardwoods (Cedar, Southern beech and
treatment of wood surface prior to the application of African Teak).
clear top coat can effectively extend the protection INTRODUCTION
of lignin from UV light degradation.
Waterborne clear coatings have been developed
Eversorb® AQ, a blend of UV absorber and HALS, is to address the concerns of high VOC that are
developed by Everlight Chemical Industrial Corporation normally associated with conventional solvent-based
(ECIC) specifically for waterborne clear coats. coatings . Most customers use waterborne clear
[1]
Eversorb® SB, designed for wood pretreatments, can wood coatings to protect wood materials. However,
protect lignin from UV light degradation. sunlight and UV radiation can penetrate coatings
For Eversorb® AQ, the effect factor of wood on wood surface, causing yellowing. The yellowness
protection ability was about 14.69%. For Eversorb® comes from both coating and lignin. Wood, as a
SB, the effect factor of wood protection ability was composition of lignin, cellulose and hemicelluloses,
about 13.35%. Eversorb® AQ and Eversorb® SB appears to yellow due to the photodegradation
have interaction effect. The effect factor is 10.9%. of lignin [2-6] . Photodegradation route of lignin [7-8] is
Both Eversorb® AQ and Eversorb® SB provide good shown in Figure 1.
performance for wood protection. Eversorb® AQ is a waterborne light stabilizer. Eversorb®
This paper is a comparison study using accelerated SB is a lignin stabilizer designed for wood pretreatments.
weathering method to test different wood types Test data confirmed that increasing the concentration
pretreated with or without Eversorb® SB in different of Eversorb® AQ in the clear top coat can effectively
co-solvents. Design of Experiment (DOE) was used protect Southern Pine from UV light degradation. Further
in this study. Our data confirmed that pretreatment experiment shows that the pretreatment on Southern
with Eversorb® SB gives better performance in UV Pine with Eversorb® SB prior to the application of clear
light degradation test. Lignin is a complex organic top coat provides better weatherability than the one
polymer containing hydroxyl functional groups (-OH). without Eversorb® SB pretreatment.
Two types of co-solvents, isopropyl alcohol and Furthermore, data also suggested that by increasing
butyl carbitol, are tested in the system, the solubility the coating thickness, the light fastness of Southern
parameters are 11.5 and 9.9, respectively. After Pine can also be improved to some degrees, but not
weathering test, Eversorb® SB mixed with isopropyl as effectively as other methods such as increasing
alcohol gives a better result than butyl carbitol. the dosage of light stabilizers in the clear coat or
Figure 1: Route of photodegradation of lignin. pretreating the Southern Pine prior to the clear
[9]
coat application . Lignin is a complex organic
polymer containing hydroxyl functional groups
(-OH). To check if solvents can affect the protection
performance of Eversorb® SB, different co-solvents
are mixed with Eversorb® SB in the experiment.
Theoretically, Eversorb® SB pretreatment can
have better performance on softwoods than on
hardwoods due to higher lignin content. Softwoods
contain 25–35% lignin and hardwoods contain
18–25% lignin [10] . The subjects of this paper are
5 different types of woods, including softwoods
(Southern Pine and Douglas fir) and hardwoods
(Cedar, Southern beech and African Teak).
EXPERIMENT
The three model formulations used in this study
were an acrylic-based waterborne clear coating,
wood pretreatments and co-solvents. Their detail

24 Journal of Surface Coatings Australia • February 2019